Freeze-thaw indicator



Dec. 24, 1963 R. D. FENlTY ETAL 25,499

FREEZE-MW INDICATOR Original Filed July 18, 1957 MIX EQUAL VOLUMES WITH STRONG AGITATION GEL PRODUCT (MAY BE CUT TO DESIRED SIZE AND FORM) 9 1 PACKAGE HAS BEEN THAWED IF "H' INDISTINCT PACKAGE HAS BEEN THAWED IF 'H' INDISTINCT INVENTORS 20884?! D. FZ'NJTX Y J01! I. amus'szw A TTOPA/E) United States Patent 25,499 FREEZE-THAW INDICATOR Robert D. Fenity, Orono Township, Hennepin County, and John E. Janssen, St. Louis Park, Minn., assignors to Minneapolis-Honeywell {egulator Company, Minneapolis, Minn a corporation of Delaware Original llo. 2,955,942, dated Oct. 11, 1960, Ser. No. 672,811, July 18, E57. Application for reissue May 16, 1962, Ser. No. 1917,22 1

5 Claims. (Cl. 9--192) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

The present invention relates generally to a condition responsive device arranged to indicate when a certain upper or lower temperature limit has been reached or exceeded, and more particularly to such an apparatus which is arranged to irreversibly visually indicate when the contents of a frozen food package has exceeded a certain temperature limit, this limit generally falling at 32 F. or below. Apparatus of this sort are designed to indicate whether or not the contents of a frozen food package have been warmed to a certain temperature for a sutlicient length of time to cause deterioration to an undesirable or dangerous point of spoilage. Inasmuch as the spoilage of frozen food is generally quite rapid at temperatures at or near 32 F. and above, it is normally quite desirable to have a reliable condition responsive device physically associated with the frozen food package and arranged to indicate any unfavorable temperature exposure history. Since the device is irreversible in its indication, any rcfreezing of the contents will not cause the indicator to revert to its previous condition.

in the past, it has been proposed to make devices for this purpose by various means. Among these include the preparation of a chemical indicator positioned at one extreme on an absorbent material such as a blotter or the like, while at the other end there is placed a treated material which is arranged to traverse the length of the absorbent material and the treatment being such as to cause a change in color in the indicator upon thawing of the treated material. Among other schemes are the use of fugitive figures which are destroyed upon melting, enzyme-indicator combinations which are arranged to change color upon exposure to certain time-temperature conditions. With virtually all of the prior art devices of this sort, it has been necessary to manufacture and store the indicators under special environment, such as at a low temperature, prior to use, these indicators requiring substantially the same refrigeration as the frozen food upon packaging. it is readily apparent that such a practice carries with it certain disadvantages in manufacture, storage, packing, and the like, and consequently are economically unsound.

According to the present invention, a frangible matrix body is provided with a certain amount of interstitial liquid which has a physical characteristic of expansion upon freezing. in this connection, a silica gel body may be prepared, the gel body including a certain amount of interstitial water. This body is then encapsulated in a suitable enclosure or envelope to prevent desiccation and provide physical protection and may be stored at ordinary room conditions until needed. The device is triggered when initially frozen, that is the gel structure appears to be ruptured by the expansion of the interstitial liquid, in this case water, the freezing of the water assisting the gel in retaining its shape or configuration until thawed. Upon thawing, the structure having previously been disassociated irreversibly disintegratcs into a shapelcss mass such as a ball of gelatinous fluid or the like. Devices of this sort are extremely inexpensive to fabricate,

" ice are non-toxic in nature, and may be treated with certain salt solutions or the like to have certain selected melting or die integrating temperatures. When encapsulated in a polyethylene container, envelope or the like, the devices do not have to be maintained in any particular or unusual atmospheric condition prior to packaging.

It is therefore an object of the present invention to provide an irreversible visual indicating apparatus for frozen food packages or the like, the apparatus not requiring storage at or under any particular atmospheric condition prior to use.

It is a further object of the present invention to provide a silica gel freeze-thaw indicator which is inexpensive to fabricate, harmless and non-toxic in nature, the melting temperature of the gel body being pre-selected.

Other and further objects of the present invention will become apparent upon a study of the following specificalion, appended claims, and accompanying drawings, wherein:

FIGURE 1 is a flow sheet of a preferred process for preparing devices for use in accordance with the present invention;

FlGURE 2 is a partial perspective view of a frozen food package including an encapsulated device prepared in accordance with the present invention; and

FIGURE 3 is a view similar to FIGURE 2 showing the device of the present invention in thawed condition.

According to the preferred modification of the pres ent invention the freeze-thaw indicator is prepared from a solution of alkaline silicate such as sodium silicate, or an alkaline earth silicate, together with a mincral acid such as I-ICl, H 50 HNO or the like. The gels are made by the addition of the mineral acid to the silicate solution, such as for example, the addition of HCl to a solution of sodium silicate until a pH of about 8 or lower is attained. In this connection, it is desirable for operation to entrain a quantity of water in the gel structure per se in order that the el body may be ruptured or destroyed upon the expansion of the entrained water upon initial freezing thereof. The structure having been so ruptured or destroyed upon freezing completely fails upon subsequent thawing.

Specific methods of preparation are given in the following examples:

EXAMPLE 1 Reference is made to the flow sheet designated FIGURE 1 of the accompanying drawing which is a schematic description of this particular example. Solution A consists of 20% by volume commercial sodium silicate solution (SiO Na O:-3.25; density 40-42 B.) and by volume water. Solution B consists of 5.2% by volume AR. HCl solution and 94.8% water. Mix equal volumes of A and B with strong agitation during mixing. the acid being added to the silicate. Gel time is about 1 to 2 minutes, occurring subsequent to agitation and mixing. This composition calculates to about 5.2% by weight sodium silicate, 1.5% by weight HCl and 93.3% by weight H O. This procedure is preferred since a more thorough mixture can be obtained in this manner and it is more adaptable to subsequent forming of products, if desired. Further delay in gel time can be obtained by diluting this composition. It should be pointed out that although this is merely the base composition, various additives might be used to modify the color, freezing and thawing characteristics, gel strength etc. As an example of these, methyl red may be employed as a coloring agent, this material not disrupting the thaw breakdown. Alcohol, glycol or salts are examples of materials which can be added to modify the temperatures of freezing and thawing.

3 EXAMPLE 2 To 100 cc. of commercial silicate solution containing 62% H O there is added ltltl cc. of H and 26 cc. A.R. HCI. the additions being made with rapid stirring. Gelation occurs almost instantaneously. The components of this gel calculate as ll).l% by weight Na O- 3.25 SiO solids, 1.8% l-iCl, and 831% H O, the solution having a pH of about 7.

in general, the concentration of sodium silicate solids in the solution for the various gels ranges from about 1 Eli up to about ltWE. For these purposes, ordinary sodium silicates having a ratio of EH0 Na O ranging from about I to about 4 are satisfactory as raw materials.

inasmuch as the gel material on thawing after being initially triggered assumes a more or less spherical, droplike or other shapeless type form. it is generally desirable to cut a form to be used in such a manner that the inalicator has a norma form other than spherical er the like. For example. an H-form may be cut from the gel with a simple die. and a column of gel so formed may be cut into relatively thin bodies or wafers having an H cross section. In this manner it is impossible that the indicator having a length dimension which substantially exceeds the transverse dimension will resume the initial form after having been triggered and subsequently thawed. Of course. the gel maybe shaped in many other suitable manners by various methods such as by cutting. casting. extrusion or the like.

In order that the units may be relatively easily and conveniently stored prior to freezing, it is preferred that the gel body he encapsulated in a suitable envelope. hlorc specifically. the envelope should be scaled from the atmosphere by providit'ig a hermetic or vapor tight seal between the gel body and the ambient atmosphere to enable storage under any room conditions. The gel structure will then not risk the possibility of becoming desiccated. more highly saturated. or otherwise harmed prior to use. Of course. if desired. the gel bodies may be cut immediately prior to use and frozen within the storage package.

Reference is made to the devices described in FIGURES 2 and 3. In this connection. the freeze-thaw indicator it) includes a body 11 sealed within a polyethylene container 12. The edges of the container are sealed by conventional heat sealing methods which are well known in the art todty. As illus rated this indicator may be conveniently placed within the frozen food package in good thermal contact with the contents and exposed to view for the consume. Upon initial freezing of the package, the indicator is triggered. the gel structure being ruptured but remaining intact. (see FlGURE 2) and upon thawing the H-cross section assumes the form of a shapeless mass (see FEGURE 3). The consumer will then be a are of the storage history of the packaged product, this history being either satisiictory or unsatisfactor It Will be noted from the allure d "ription that the units remain unchanged prior to free mg rim! that the indication t'lUiS not occur until flit? purl-(aged prmln'tl has been frozen and flier: than-ed. For this reason, (1S ptn'ntcil our in the inrrori'ucrimz, the apparatus is usefnl for indicating trite/i (a curtain lower temperature limit has been reached as well (1.8 for when an upper temperature limit is r. 'cceu'erl. Thus where this [rulii'a'ri' r is" meal with (a pm. kt'igeel product tlmt is not normally subjected to freezing conditions, the indicator indicates u'lwtlicr l'ltt' par/.trccd prmluct has been frozen and Illt'f! Ill-'lli'tll.

Of course, other embodimcn s may be made of the present invention without departing from the specific structure of the present invention. It will be understood, therefore. that the specific embodiments given are only intended to be illustrative and we are to be limited only by the scope of the appended claims.

We claim:

El. The method of arran ring for an indication of exposure of the contents of a frozen food package to thawed conditions which method comprises placing an eucap sulatcd frangible silica gel matrix body having interstitial wa er retained therein into close proximity with said conte is, and subsequently freezing said frangible silica gel matrix body. thereby substantially destroying the gel structure thereof] The method of arranging for an indication of exposure of the contents of a frozen food package to thawed conditions which method comprises placing an encapsulated frangible silica gel matrix body having in terstitial water retained therein and having a mass which is small relative to the mass of the said contents. into close proximity with the said contents. and subsequently ing said l'arigide silica gel matrix body. thereby substantially destroying the gel structure thereof.

" had of arrang. an

. 1m ieation of exposure of contents of a frozen food package to thav ".115 which method comprises placing an enaapsuiated irai'agible siica gel :atrix body having a water from between about lllih up to about into clo e pr ximity with said contents, and

subsequently frc Elli-f; said frangible silica gel matrix body,

thereby a tlly destrc-yirg the gel structure thereof E4. ile method of arranging for an intlt' uion of exposure of the contents ol a frozen food package to thawed conditions which method comprises placing an encapsulated frangible silica gel matrix body having a distinct phy cal form and having interstitial water retained therein into close proximity with the said contents. and subsequently l'reaing said frangible silica gel matrix body. thereby substamially destroying the gel structure thereof] 5. The met/mil of arranging for rm indication of exposure of a package to freezing and to .SlllJSL'fflltfZl/jt than-m! ct' ar."' which met/mil cmnni'isc's forming (I silica gel matrix body containing interstitial water into a configuration such that the length of a portion thereof is greater than the lrcnt'aersc dimension of said portion, encapsulating said body in a transparent water-impervious envelope, raid envelope being substantially larger in the transverse dimension of mi d matrix body than said matrix l'rody so that when said hotly is frozen and subsequently thawed it is free to deform transversely within said erlvclope, and placing said envelope into close proximity tt'irlt said przt'kn v, uwiri'cliy ttlllJit lt 'iiif freezing and Illf'lltlilf, of said matrix body provides visual indication that alter/mic freezing and lllttlt'illf of said package has taken place.

6. The method of arranging for an indication of exposure of a package in freezing and to subsequently tlunvecl conditions which met/10d comprises forming a silica gel matrix body containing interstitial u 'ater into a configuration such that the length of a portion thereof is greater than the transverse dimension 0) said portion, encapsulating said body in a transparent n'nfer-impervious envelope, said envelope being substantially larger in the transverse dimension of said matrix body than said mar/ix body so that when suit! body is frozen am! subsequently tlzntvc'd it is free to deform transversely within said envelope, the mass of said body being small relative m the mass of said package, and placing said envelope into close proximity tt'l'tli said package, whereby subsequent freezing (51:11 ll l' llt' or" will matrix hotly provides (l visual indication tlmt alternate freezing and tliruring of mid package has taken place.

7. The met/mil of arranging for an indication of CI posm'c 0/ u put/cage to [ree ing and to sulucq1nIit/ v thawed conditions which metltod comprises forming a silica gel matrix body having a water content between about 90% up to about 99% into a configuration such that the length of a portion thereof is greater than the transverse dimension of said portion, encapsulating said body in a transparent water-impervious envelope, said envelope being substantially larger in the transverse dimension of said matrix body than said matrix body so that when said body is frozen and subsequently thawed it is free to deform transversely within said envelope, and placing said envelope into close proximity with said package, whereby subsequent freezing and thawing of said matrix body provides visual indication that alternate freezing and thawing of said package has taken place.

8. A device for indicating whether a freezing and subsequent thawing has taken place comprising a transparent water-impervious material defining an enclosed container, a silica gel matrix body containing a quantity of interstitial water retained therein enclosed within said container, said matrix body having a configuration such that the length of a portion of said body is greater than the transverse dimension of said portion, said container providing a cavity substantially larger in the transverse dimension of said matrix body than said matrix body so that when said body is frozen and subsequently thawed the body is free to deform in the transverse direction within said container.

9. A device for indicating whether a freezing and subsequent thawing has taken place comprising a transparent water-impervious material defining an enclosed container, a silica gel matrix body having a water content ranging from about up to about 99% retained therein enclosed within said container, said matrix b dy having a configuration such that the length of a portion of said body is greater than the transverse dimension of said portion, said container providing a cavity substantially larger in the transverse dimension of said matrix body than said matrix body so that when said body is frozen and subsequently thawed the body is free to deform in the transverse direction within said container.

Sears Nov. 13, 1951 Smith Dec. 8, 1953 

